Indirectly heated cathode



Jan. 17, 1939. G. JOBST INDIRECTLY HEATED CATHODE Filed Nov. '7, 1936 wmo J R E m NN IE ATTORNEY Patented Jan. 17, 1939 UNITED STATES PATENTOFFICE INDIRECTLY HEATED CATHODE raphic in. b. H., Berlin,

tion of Germany Germany, a corpora- Application November 7, 1936, SerialNo. 109,621 In Germany November 7, 1935 4 Claims.

In indirectly heated cathodes the flow of heat from the filament to thesurface of the cathode causes a temperature gradient from the heatingWire to the outer shell which is greater the larger the required heatinput and the poorer the heat transfer from the source of heat to thesurface. High temperatures in the interior or" the cathode entails anumber of disadvantages, such as disintegration of the insulation andheating Wire material.

The present invention avoids these difiiculties by reducing thetemperature difference between the heater and exterior of the cathodewith its electron emissive coating by a good heat conducting medium suchas a metal intermediate wall in good heat conducting relation with theheating Wire and with the cathode cylinder or sleeve. The metalintermediate Wall may act as a rigid support for the hot filament.

According to the present invention, the insulating layer electricallyseparating the heating Wire from the metal intermediate Wall is made asthin as feasible to insure proper electrical insulation and good heatconduction between the wire and the Wall. It is known that theinsulating property of most insulators is better at lower temperatures.The heating wire may be coated with insulating material and supported onthe intermediate Wall or upon supplementary supporting means. To disposegreater lengths of heating Wire in the cathode it is preferable toprovide a meander-formed arrangement of the insulated heating wire onthe intermediate Wall. The cathode may be elliptical in cross-section onthe major axis of which is placed the intermediate wall.

The intermediate Wall may be curved at its .edge, and the curved portionof the Wall held in good heat conducting contact with the inside surfaceof the cathode sleeve. A supporting and centering pin for the cathodeassembly may be attached to the intermediate wall. The temperaturedistribution throughout the length of the cathode may readily becontrolled by properly arranging the heater Wire on the intermediatewall.

The characteristic features of this invention are set forth in theappended claims and preferred embodiments thereof and are described inthe following specification and shown in the accompanying drawing inwhich:

Figure 1 is a cross-sectional View of a core assembly ready forinsertion in a cathode sleeve;

Figure 2 is a perspective view of an assembled intermediate wall andheating wire constructed in accordance with this invention;

Figure 3 is a cross-sectional view of another cathode core constructedin accordance with this invention;

Figures 4 and 5 are perspective views of another intermediate wall andheater wire assembly of this invention; and

Figure 6 is a perspective View of an electrode mount showingfragmentarily the novel cathode core assembly of this invention securedin its proper spaced relation to the other electrodes.

The core assembly shown in transverse crosssection in Figure 1 withoutthe cathode sleeve, comprise heating wires H enclosed by an insulatingcoating or layer S1 and bearing against the intermediate Wall W, theedges of which are curved on a radius equal to the radius of the insideof the cathode sleeve. A second insulation S2 is filled into the spacedefined by the wall, its outer surface being rounded on the same radiusas the edge portion of the wall. The assembly of Figure 1 may beinserted in a cathode sleeve with the wall edges in good heat conductingcontact With the sleeve. The intermediate wall and the bent edgesmechanically stiffen the core assembly and protect the insulation duringmanufacture.

Figure 2 shows the intermediate or separating wall in perspective withinsulated heating wire H disposed on the wall and stretched lengthwiseof the wall in several V formations. Insulation S2 has been omitted inthis figure for the sake of clarity.

Figure 3 shows a core elliptical in cross-section with a surroundingshell or sleeve N exteriorly sensitized with an electron emittingcoating and Which bears snugly against the bent portions of separatingwall W and the insulating filler S2 of the core. In this embodiment ofthe invention the heating wire H, as shown in Figure 4, is laidmeander-like against the wall W. The wall W at those portions of itssurfaces that face the heating wire is insulated by layers S3.

In Figure 5 insulated heating wire is wound bifilar on the metallicplate of the separating wall W and is held at the edges of the plate innotches V. The sides of the wall may be insulated if desired, and thecore assembly may be filled and rounded out with insulation for easyinsertion in cathode sleeve N.

Figure 6 shows means for supporting the heating element in an electrodeassembly and, for convenience of illustration, the filler for the coreand theouter shell and the grid of the tube have been omitted. Thecathode core assembly is supported at its lower end by wire D embeddedin the press and fastened to the intermediate wall and at the upper endby a guiding pin F in an insulating strip G such as of mica that issupported by anode stays A.

I claim:

1. An indirectly heated cathode for electron tubes comprising acylindrical metal sleeve exteriorly sensitized with an electron emissivecoating, an insulated heater wire in said sleeve extending throughoutthe length of the sleeve, and means for efficiently conducting heat fromsaid wire radially outward to the Wall of said sleeve comprising a metalwall of good heat conductivity in the sleeve and extending across thesleeve throughout the length of the sleeve and good,

thermal contact with the insulated wire and with the interior andintermediate the ends of the sleeve.

-2.,An' indirectly heated cathode for electron tubes comprising athintwalledcylindrical sleeve exteriorly sensitized with, electronemisssive, substance, a heating assembly in said sleeve comprising aheater wire and a metal wall, of. goodv heat conductivity, said;wallbeing in good: thermal contact with the interior of the sleeve at spacedpoints throughout the length of the sleeve, and the wall being coveredwith insulating material and the heating wire supported in grooves inthe insulated wall.

3. An indirectly heated cathode for electron tubes comprising a thinwall cylindrical sleeve exteriorly sensitized with electron emissivesubstance, a heating assembly in said sleeve comprising an insulatedheater, wire and a metal wall of good heat conductivity, said wall beingbent at its edge on a curvature the same as the curvature of the innersurface of said sleeve and in good heat conducting contact with thesleeve, said wall being in good thermal contact with said insulatedheater wire.

4. An indirectly heated cathode for electron tubes comprising a thinwalled cylindrical sleeve exteriorly sensitized with electron emissivesubstance, aheating asembly within said sleeve comprising an, insulatingheater wire and a metal Wall of good heat conductivity, said wallextending' across the interior of the sleeve and being in ood thermalcontact with said insulated heater Wire and in, contact with the sleevesubstantially throughout its length to provide a uniform temperaturedistribution along said thin walled sleeve.

GUNTI-IER JOBST.

